Melatonin action on pineal varies with photoperiod.
D000818:Animals; D002940:Circadian Rhythm; D005260:Female; D008027:Light; D008550:Melatonin / Q000494:pharmacology*; D010507:Periodicity; D010870:Pineal Gland / Q000378:metabolism* / Q000528:radiation effects; D011830:Radiation Effects; D051381:Rats; D012701:Serotonin / Q000378:metabolism*
D012701:Serotonin; D008550:Melatonin